1. Field of the Invention
The present invention relates to a keyboard apparatus of an electronic musical instrument, and more particularly to a stopper member which restricts pivoting of keys of the keyboard apparatus and massive bodies which pivot in synchronization with the keys.
2. Description of the Related Art
In a keyboard apparatus of an electronic musical instruments, conventionally, a range in which keys are allowed to pivot when the keys are depressed (from the initial position to the maximum pivotable position) is restricted by an upper limit stopper and a lower limit stopper provided on a key frame. FIGS. 20A to 20C are right side views schematically illustrating a conventional keyboard apparatus of an electronic musical instrument. The keyboard apparatus has a white key main body 1, a black key main body 2 and a key frame 3. The key frame 3 has front and rear steps in a longitudinal direction of the keys to have a horizontal portion 3a between the steps. On the rear end of the horizontal portion 3a, a key supporting portion 3b is provided.
On the rear end of the white key main body 1, a key pivot portion 1b is provided. The white key main body 1 is fastened to the key supporting portion 3b with a key pivot portion 1b to pivot about the key pivot portion 1b. The white key main body 1 has right and left sides formed downward from the both sides of the top surface. The white key main body 1 also has a pair of right and left stopper pieces 1c provided at the midpoint near a front end 1a of the right and left sides, the stopper pieces hanging downward from the right and left sides. Front ends 1d of the stopper pieces 1c are bent approximately perpendicularly toward the depth of the key. The black key main body 2 also has a key pivot portion 2b and stopper pieces 2c on the positions similar to those of the white key. On the front step of the key frame 3, a plurality of parallel slits 3c are vertically formed so that the front ends 1d, 2d of the stopper pieces of the white key and the black key are inserted into the respective slits 3c. 
On the horizontal portion 3a of the key frame 3, a key switch 4 is provided. Projections (actuators) which are not shown are provided on the undersurface of the white key main body 1 and the black key main body 2 to oppose to the key switch 4. On the undersurface of the horizontal portion 3a of the key frame, an upper limit stopper 182 which is shaped like a stripe is arranged along the keys so that the upper limit stopper 182 opposes to the top surface of the front ends 1d of the stopper pieces 1c. On the top surface of the horizontal portion 3a, a lower limit stopper 181 is arranged so that the lower limit stopper 181 is shaped like a stripe. In the shown example, the white keys and the black keys have the same structure.
In view of shock absorbency, noise reduction and reproducibility of pivotable range, the upper limit stopper 182 and the lower limit stopper 181 are required to be formed of material having elastic recovery force. Conventionally, felt, polyurethane elastomer or the like is employed as the material of the upper limit stopper and the lower limit stopper. When a player depresses a key, the key switch 4 is elastically compressed to turn on a switch. When the key is further depressed, the lower limit stopper 181 is given a shock by the right and left sides of the white key main body 1 or the black key main body 2 to be elastically deformed. At the time of elastic deformation, internal friction causes kinetic energy to be converted into heat energy, resulting in damping of the key. When the lower limit stopper 181 recovers from elastic deformation, the lower limit stopper 181 produces elastic recovery force. This elastic recovery force becomes repulsion (referred to as rebound) for the key. The rebound is conveyed to the player's finger through the white key main body 1 or the black key main body 2, causing player discomfort.
When the key is released, a force which recovers the key such as action of a recovery spring which is not shown causes the white key main body 1 or the black key main body 2 to return to its initial position. When the key returns, the top surface of the front ends 1d of the stopper pieces 1c collide with the upper limit stopper 6. At this collision, an elastic recovery force of the upper limit stopper 6 becomes repulsion for the white key main body 1 or the black key main body 2. Since this repulsion is exerted toward the direction opposite to the force which recovers the key, the white key main body 1 or the black key main body 2 vibrates until the key fully stops. If the player's finger touches the key, as a result, the vibration is conveyed to the player to cause discomfort.
In addition, there has been a conventional keyboard apparatus of an electronic musical instrument whose massive bodies pivot in synchronization with player's key-depressions to provide the player with key touch close to that of an acoustic piano. The upper limit of a pivoting massive body is restricted by a collision of the vicinity of a rear free end of an inertial moment generating portion with an upper limit stopper. When a key is released to return to its initial state, the position of the massive body is restricted by a collision of the vicinity of the rear end of the inertial moment generating portion with a lower limit stopper. The upper limit stopper and the lower limit stopper provided for the above-described massive body also absorb shock of inertial moment of the massive body to damp the massive body. The upper limit stopper produces a repulsion when the massive body is driven to collide with the upper limit stopper, while the lower limit stopper produces a repulsion when the massive body recovers to collide with the lower limit stopper.
In an invention disclosed in Japanese Patent Laid-Open No. 2003-195853, for an upper limit stopper provided for hammers (massive bodies), a “massive portion MB” is provided along with the upper limit stopper. In the “massive portion MB”, a massive body is sandwiched between a lower cushion and an upper cushion. This massive body is made of elastic material made by blending elastomer or rubber with metal powder so that the material has an appropriate mass and flexibility. In addition, Japanese Patent Laid-Open No. 2003-195853 also discloses that the “massive portion MB” may employ a chain metal wire or a member formed by packing sand or metal powder in a pouched member so that the member has the same width as the entire width of the keys or the width of a plurality of keys. The “massive portion MB” is fastened to a rear part of a chassis by bonding or the like, or is held by enfolding the “massive portion MB” from below upward with a sheet member.